Four component optical objective



June 24, 1952 G. H. COOK 2,601,595

FOUR COMPONENT OPTICAL OBJECTIVE Filed March 15, 1951 2 SHEETS-SHEET 1 F/ 3 R5 R 7 R8 Inventor GORBGN H. (10011 Attorney June 24, 1952 G. H. COOK 2,601,595

FOUR COMPONENT OPTICAL OBJECTIVE- Filed March 13, 1951 2 SHEETS-SHEET 2 4 R6 R7 F/G 4 R3 #2841 -7692 --3a7 Inventor G-ORDou c. 00

-o y I 32 028 g M u 6% Attorney Patentecl June 24, 1952 UNITED STATES PATENT OFFICE.

2,601,595" FOUR COMPONENT OPTICAL OBJECTIVE- Gordon Henry Cook, Leicester; England; as signer to. Taylor, Taylor-sit Robson.- Limited; Leicester, England, a, British company Application March 13, 1951.'SerialNm2i5255 nr Grew t Britain Februaryfl'K, 1951;

11: Claims. (0138 -57) 1 This invention relates to an optical objective, more especially for photographic purposes; corrected for spherical and: chromatic aberrations,

coma,- astigmatism, field curvature'and distortion, and comprising two simple convergent componcn ts located between two divergent doublet componentseach consisting of a convergent element and. a divergent element; all fourcomponents being of meniscus form with their air-exposed'surf-aces concave towardsa diaphragm between the two simple components, the divergent element in each compound.v component being on s d e re t e diaphragm vention of the-present applicants-co.-

Dflding app1ication .of the United State'sl of.

America No. 2 14508., fi'ledMarch '8, 1951, is concerned' witha walk-corrected objective of this type "avingfla high-relative aperture and wide eoverm iqpower-end aiso having: improved cor rectioii forzonalsphefical aberration andobl'iqjue. sphericaliaberration, such invention having the advantage. that it makes it jpossibie 'to o ameterszjiarcer than are needed forthe alone'in order avoidthe vignetting' wh'i wouidother wide" angular field vere In the objective a'ecordingtosucn copenaiing application, as alsointheobiective according to the present applicatiomth'e-arithmetic mean between thecurvatures of the internal contacts in th ones for-this. purpose "aspositi've when the internal contact-isconcave" towards. the "dia phi-semi: is'ies'sfthan 3.5 times theequivaieht power of the, objective and is greater than flier /(iozc+i J times such equivalent power; where is the positive value-of the tinfe'rence between thearithm'etic mean of the mean refractive indices of the materials'of the COIL-P versenteleinents-of "the. doublet components and the arithmeticifnean the-mean refractive indiscs of the materials *o f the or such component's.

'ifh e-tei-rri internal contacts is used herein,

in'orderto? avoifdthe ambiguity andoonfusion inlierentin' the use'ofthe terms internal contact surface"? ami-internaicontaet surfaces more use pound component, whether such surfaces are eemented together or are in the form of a broken contectfwhat-ia when the'two cooperating surioees have slightly fdirferentcurva tures.-' such cu-- ierence 'beingie'ss' than 0.2 times theeqdivaient mean-"between thereon or curvatureor the two sunfieesain' the case for-a broken contact.

' The invention of such copending application i'ecti'onable with the "e'- ;do' db1etcuterieonaponents (a curvature being divergent elements" by employed hitherto, and indicates-thee'sseinblageof two cooperating surfaces in a com- 1 any) crime two surfaces is Jess than oi ..-dom of choice of theindices.

a higher degree. of correction-routine various aberrations but witha smallercovering power.

' In this modification according to the present.

invention, the objective corrected. to cover :a

semisangular field not greater than 30: degrees has Petzval curvature between. .O8and .16times. the equivalent'opticalipower of. the objective, the term Petzvalcurvature being used in its. usual.

significanceto denote the sum for all. the surfaces of-the objective of the product of the curve.- ture of asurface andthe-difierencebetweenthe reciprocals of the mean refractive indicesof the materials in front of and behind the surface, such difference being reckoned. as positive if the material behind the surface has greater index than that in'front of the surface, whilst the curvature is for this purpose reckoned as positive if the surface is convex to the front in accordance with the usual. convention. Expressed mathematically, thelPetzvalvcurvature isdefinedby the expression 21(N N)/N .N.R, Where N and N are respectivelythe mean'reiractive indices of the materials behind and in. front of the surface and R is the radius of curvature of the'surface, the symbol 2 indicating the'sum of the values of the following expression for-all the surfaces of the objective. The. terms front and rear are used herein in accordance with the usual =convention to denote the sides of the objective respectively'nearer to and further from the longer conjugate.

The arithmetic mean between the axial thicknesses of the two 'dou'blet'components preferably lies between .075 F and .15 P where F is the equivalent focal length of the objective. The arithmetic mean between the positive values of the radii of curvature ofthe. outer surfaces of the simple inner components preferably lies between .22 'F'ancl .44 F. The arithmetic mean betweenthe positive valuesfof the radii of curvature of the inner air-exposed surfaces of the two doubletcomponents preferably lies between .11 F and 25 1 The arithmetic mean between the: pos itive values of'the radii of curvature of the outer air-exposed :s'u'rfac'esof thetwo doublet components preferably lies between .17 F and .30 F.

Since the expression 2('10a:- 1)./(l0a:+.1), referred to aboveycan be "negativ the invention does not preclude the possibility of having the internal'contacts in the doublet components canvex towards the diaphragm, butzthisis only per missible provided that the refractive index differences between the convergent and divergent elements of the doublet components are small.

On the other hand, since pression'cannot exceed 4 2, and consequently, if the internal contacts are fairly strongly con'' cave towardsv the diaphragm, there is wide freea: is positive, such ex- In one group of practical embodiments of the invention'fa: as above defined is less than .025," and the arithmetic mean between the mean reiractive indices of the materials pf the two simple components lies between 1.60' and 1.80.

In another group of embodiments of the invention, a; is greater than .025 and the arithmetic mean between the mean refractive indices of the materials of the two simple components lies between 1.55 and 1.68, the arithmetic mean be tween the mean refractive indices of the materials of the convergent elements of the two doublet components being greater than that of the divergent elements in such components.

Figures 1-'7 oi the accompanying drawings respectively illustrate seven convenient practical examples of objective according to the invention and numerical data for these examples are givenin the following tables, in which R1R2 represent the radii of curvature of the individual surfaces of the objective, the positive sign indicating that the surface .is convex to the front and the negative sign that it is concave thereto, D1D2 represent the axial thicknesses oi the various elements, and 818253 represent the axial air separations between the components. The tables also give the mean refractive indices 11. for the D-line of the spectrum and the Abb V numbers of the materials of the various elements.

I Example I Equivalent focal length 1.000. Relative Aperture F/4 Thickness or Abbe V Refractive Radius Air Separa- Numtion 7 Index m) ber Di=. 040 1. 700 30. 3 R|=+.1686

, S =.O274 R4 2717 D==. 03 l. 691 54. 8 Rs =.+.4407 S:=. 041 Rs 6345 Sz=.0316 Rs 1949 Ds=.035 1.700 30.3 R =-.4938 Du=.055 1.700 41.2

Example II Equivalent focal length 1.000. Relative Aperture F/i' Thickness or R ti Abb V Radius Air Separa- 9 ac Num- 1 tion Index ber Dz==. 020 1. 700 41. 2 R: 1686 l Da=. 030 l. 691 41. 2 R. .4407

Sg=- 041 R9 .6345

. D D455 1. 691 41. 2 R .3521 Y i -S;=.0316 a 1949 D= 020 l. 700 41. 2 R, =+1. 0194 j a v Da=.070 1.700 53.0 a

Exempt 2H1. 1. Equivalent focal length 1.000. Relative Aperture F/4 Thickness or Abbe V Refractive Radius An Separa- Numtion Index ber S1= 026 R g0 v D =.'030, L691 54.8 Rb =+.4444

S2=.056 .R6 =-.7194 v D D38 1 691 54.8 R =-.3717 J g Y Sa=.028 R5 1930 D5=.040 1.623 36.0. R9 F 4762 Da=. 060 1. 623 56. 2 Rw=-. 2315 to cover a semi-angular field of 25' degrees in Example I, 25 degrees in Example'II and 28' degrees in Example III. The Petzval curvature is .099in Example I, .099 in ExampleII and .135-

I in Example IILtimes the equivalent powerot the objective.

All three examples belong to the first of thetwo groups above mentioned, andsince the'materials of the convergent and divergent elements of the two doublet components have substantially. the same mean refractive index, a: as above definedis zero, so that the expression has the value" 2 in each case. This permits."

according to the invention'a wide choice in the curvatures of .the'inteinal contacts R; and R9. There is also'available'a wide choice' of Abbe Vj v numbers for the materials of all theelements.

numbers.

phragm, and the arithmetic mean between themj This'considerably simplifies the problem of finding suitable materials for the elements and also greatly iacilitates'correction of the higher: order chromatic errors.' f'

Thus, in Example I the internalcontacts R2 and R9 are'both fairly strongly concave towards the diaphragm, whilst Example II is a modification of Example I, in which the internal contacts are slightly convex towards the diaphragm and in which a completely difierent series oi Abb'" V numbers is used. Example III again has its in-' ternal contacts fairly strongly concave" to th'e. diaphragm, but differs from Example I in having lower refractive indiees in the doublet components and yet another different series of Abbe Vi In Example I the curvatures of-the internal. contacts R2 and Re are respectively +2.5 and +2.0, the positive sign in this case indicating. that the surfaces are concave towards the diais thus +2.25. In Example II. the corresponding figures for the two curvatures are +0.14 and, 0.98 giving an arithmetic mean +0.56, whilstin Example III the curvatures are +2.8 and +2.1;

giving an arithmetic mean +2.45. Thesefigures are in terms of the equivalent powerof theobjec- 1 tive. "1 1 a r The: arithmetic mean. between the axial: thicknesses: of the two doublets'is'..095 FinExamples Ia and II and .105 I -in Example: III, where F isthe. equivalent i'ocal. length of-the. objective. The

arithmetic mean between the positive values of the radii of curvature of the outersuriaces R4 and R1 of the: simple inner components is .3119 F in; Examples I and II and .3259 F in Example-III. The: arithmetic mean between the positive values of the radii: of curvature of the inner surfaces R's-and R1 of the doublet component's .1818 F in ExamplesI and II and .1801 F in Example III. The arithmetic mean'of the positive values of the radiiof curvature of the outer surfaces-R1 and Rio of the doublet components is .2313 F in'Ex amples I: and 11 and .2294-F in Example 1T1.

Emmpi Iv Equivalent focalv length 1.000. Relative u 7 Aperture F/3. 6

F. .1 Thickness or Abb V Radius Air Separagggfi g Numtion' bet.

R .2326 v w D1.=..070 6570 50.8.- R, .51s5 13.2%.040 1.6205} 36.2 Ba =.I. .169. 81.5028 I R. e+ .2841. Y

. D3=. 022 1. 234 56, 2 R .4525 A Sci-5.051-

D4=. 036 1. 623g 56. 2 t 31: .3876- s=--Q R .1961 I I 115:...040 1. 6055 38.0.

Da=. 060 1. 6570' 50:8 B105"? .2419

Examp e V Equivalentfccal. length 1.000.. Relative Aperture F/4 Thickness or Abh V Refractive Radius A1r Separa- Nummm Index no. hey

R -i-. 2473 I D1=..0 80, 1. 7000 41.2 R2=+L5385 I D23. 03f) 1. 6518( 33; Rs=+ 1754 S1=.O25 B -k @58 $2=-0 Ra 6439 4 D4= 05D 1-. 5887' 61. 2

S'z=..03l Ra==- .2070 a v Di=- 3 5430* 1 3. 3 a,=-4.0oq 0 Ds=1070 l. 7000 41. 2. 319 508 Invthese two examples the diaphragm is 1ocat-- *lhesetwo examples belong to the; second of the scope of the inventio the twov groups, wherein. .r' as above. defined; is greater than .025. In- Example IV, :0: is .044. and. the expression 2(10a:1)/ (10:1:+1) works out as .81, the corresponding figures for Example V being .052 and .63. In Example IV the curvatures of the internal contacts R2 and Rs; in terms of the equivalent power of theobiective, are respectively +1.94- and +36; thecontacts both being concave. to the diaphragm, and the arithmetic: mean between. them is thus +1.40. The corresponding figures for Example V are. respectively +55 and +25 giving: a mean +45.

The arithmetic mean between. the axial: thick.- nesses of the two doubletsv is .105. E inboth ex.- amples. The arithmetic-mean between the posttive values of the radii of curvature oi the outersurfaces R4.- and R1 of the simple inner come. ponentsis .3358 F in Example IV and .3112 Fin Example V. The arithmetic mean between. the.-

positive values of the radii of curvature: ofthe.

.-. outer surfaces Ri'and R10 of the doublet com: ponents is .2372 E in Example and .2540. F in Example V.

In all the foregoing examples, the two halves of the objective are nearly symmetrical with one another, but this is not essential to the invention, and various combinations of one half of one example with one half of another example, with relativelyslight; consequential alterations of me i the diluent s. are pqssibl within 11. Again, it is sometimes possibleto modify such variants further by interchanging the refractive indices of two corresponding elements, one in each half.

Thus the following table gives, by Way of example, one such variant, in which the front half closely resembles that of Example III and the rear half that of Example IV.

Example VI Equivalent focal length 1.000. Relative Aperture F/4 Thickness or Abbe V Refractive Radius Air Separa- N umtion 'be'r R 2273 D1= 070' 1. 6230; s6; 2, R;=,+. 3 571 s.=.c27, R 2778 28;-030 1. time 54, s Ri=+.4386

134:. 035V 1. e234. 56:2. R7=-.3846

S =a 029 R l-=-'=-. 6.

D5=. 040 l. 6132 36. 9. Re: Dai=. D60 1. 65.70 50. 8 R1o'= .2399.

emi-an u 266. 51 0 2 de e s- Thfi Petaval:

curvatur s 21 tim s th -equiva ent power of the objective.

. in this example,.a: as above defined has the value .0219 and the expression and R10 are respectively .3312 F, .1816 F and.

In all the foregoing examples, the internal contacts are cemented, but as has already been mentioned, this is not essential to the invention, and .either or both of the internal contacts may be in the form of broken contacts. As one example of this, the following table shows a variant of Example IV, in which the internal contact in the rear doublet component is'a broken contact, that in the front doublet component being cemented.

Eata'mple VII Equivalent focal length 1.000. Relative Aperture F/3.5

Thickness or Abbe V Refractive Radius Au Separa- Numfiop Index 'nn ber D1 070 1.6570 50.8 Ra 5165 Da= 040 1.6205 36.2 R: 1695 D==. 032 l. 6234 56. 2 R5 4525 Sa=. 051 R 7692 Ss=.028 RI 1961 D5. 040 1.6055 38.0 R =-l.l628

84 005 Rio= 1. 1655 Da=. 052 1. 6570 50. 8 R11 2412 The diaphragm in this example is approximately midway between the surface R and R6, and the objective is corrected for a semi-angular field of 25 degrees. The Petzval curvature of the objective is .120 times the equivalent power of the objective.

In this example 1 has the value .044 and the expression 2(10x-1) /(l0:v+1) the value -.3l. The curvature of the cemented contact R2 is +1.94 times the equivalent power of the objective, whilst that of the broken contact R9 R10 is the mean of the two individual curvatures +.86 times such power, so that the arithmetic mean between them is +1.40 times such power.

The arithmetic mean between the axial thicknesses of the two doublet components is .105 F. The arithmetic means between the positive values of the radii of curvature of the surfaces R4 and R1, the surfaces Re and Rs and the surfaces R1 and Rn are respectively .3358 F, .1828 F and .2869 I.

In all the examples, the improvements according to the invention make it possible to have larger diameters for the various elements than is required for the axial beam alone, and such larger diameters are very valuable in facilitating correction for oblique aberrations. Thus in Examples I, II, III, V and VI, the diameters of the various surfaces may be .32 F for R1 and R2, .2 F for the chamfer diameters of R3 R5 R6 and Rs, and .28 F for R0 and Ru. In Examples IV and VII, the diameters may be .30 'F for R1 and R2, .22 F- for the chamfers Of R3 R5 R6 and R8, and .26 F for R9 and Ru (Example IV) or for R8 R10 and Rn (Example VII).

The insertion of equals (2) signs in the radius columns of the tables, in company with plus and minus signs which indicate whether the surface is convex or concave to the front, is for conformity with the usual Patent 1 O-fiice custom, and it is to be understood that these signs are not to be interpreted wholly in their mathematical significance. This sign convention agrees with the mathematical sign convention required for the computation of some of the aberrations including the primary aberrations, but different mathematical sign conventions are required for other purposes including computation of some of the secondary aberrations, so that a radious indicated for example as positive in the tables may have to be treated as negative for some calculations as is well understood in the art.

What I claim as my invention and desire to secure by Letters Patent is:

1. An optical objective, corrected for spherical and chromatic aberrations, coma, astigmatism, field curvature and distortion, to cover a semiangular field not greater than 30 degrees, and comprising two doublet divergent outer components each having an outer convergent element and an inner divergent element, two simple convergent inner components located between such outer components, and a diaphragm located between the two inner components, said components and diaphragm being air spaced in axial alinement and all four components being of meniscus form with their air-exposed surfaces concave towards the diaphragm, the arithmetic mean of the curvatures of the internal contacts in the doublet components (a curvature being reckoned for this purpose as positive when the internal contact is concave towards the diaphragm) being algebraicly less than ,+3.5/F where F is the equivalent focal length of the objective and greater than 2(l0:r-1)/(l0:c+l) F,' where a: is the positive value of the difference between the arithmetic mean of the mean refractive indices of the materials of the convergent elements of the two doublet components and the arithmetic mean of the mean refractive indices of the materials of the two divergent elements, the Petzval curvature as determined from the expression 2(N N)/N .N.R having a value lying between .08/F and .16/F where the symbol 2 indicates the sum of the values of the expression following it for all the surfaces of the objective and N and N are the mean refractive indices of the materials respectively behind and in front of the surface while R is the radius of curvature of the surface and for this purpose is reckoned as positive when the surface is convex towards the front of the objective.

2. An optical objective as claimed v v in which the arithmetic mean of the axial thickin claim 1 "9 nesses ofthe two doublet components lies between 075 F and .16 F.

3. An optical objective as claimed in claim 2, in which the arithmetic .mean of the positive values of the radii of curvature of the outer surfaces of the simple inner components lies between -.22 F and .44 F.

*4. optical objective as-cl'a-i-med in claim 3, which the arithmetic mean of the positive values o'f therad-i-i of curvature of the innermost surfaces of the doublet components lies between .11 F and .25 F, and that of the outermost surfaces of the doublet components lies between .17 F and .30 F.

5. An optical objective as claimed in claim 1, in which the arithmetic mean of the positive values of the radii of curvature of the outer surfaces of the simple inner components lies between .22 F and .44 F.

6. An optical objective as claimed in claim 1, in which the arithmetic mean of the positive values of the radii of curvature of the innermost surfaces of the doublet components lies between .11 F and .25 F.

7. An optical objective as claimed in claim 1, in which the arithmetic mean of the positive values of the radii of curvature of the outermost surfaces of the doublet components lies between .17 F and .30 F.

B. An optical objective, corrected for spherical and chromatic aberrations, coma, astigmatism, field curvature and distortion, to cover a semiangular field not greater than 30 degrees, and comprising two doublet divergent outer components each having an outer convergent element and an inner divergent element, two simple convergent inner components located between such outer components, and a diaphragm located between the two inner components, said components and diaphragm being air spaced in axial alinement and all four components being of meniscus form with their air-exposed surfaces concave towards the diaphragm, the arithmetic mean of the curvatures of the internal contacts in the doublet components (a curvature being reckoned for this purpose as positive when the internal contact is concave towards the diaphragm) being algebraicly less than +3.5/F where F is the equivalent focal length of the objective and greater than 2(10a:-1)/(10:t+1)F, where a: is the positive value of the difference between the arithmetic mean of the mean refractive indices of the materials of the convergent elements of the two doublet components and the arithmetic mean of the mean refractive indices of the materials of the two divergent elements, the Petzval curvature as determined from the expression E(N -N)/N .N.R having a value lying between .OS/F and .16/F where the symbol 2 indicates the sum of the values of the expression following it for all the surfaces of the objective and N and N are the mean refractive indices of the materials respectively behind and in front of the surface while R is the radius of curvature of the surface and for this purpose is reckoned as positive when the surface is convex towards the front of the objective, the said difference a: being less than .025 while the arithmetic mean of the mean refractive indices of the materials of the two simple components lies between 1.60 and 1.80.

9. An optical objective as claimed in claim 8, in which the arithmetic mean of the axial thicknesses of the two doublet components lies between .075 F and .16 F.

I0. An optical objective as claimed in claim 8, in which the arithmetic mean of the positive values of the radii of curvature of the outer surraces of the simple inner components lies between .22 F and .44 F.

11. An optical objective as claimed in claim 8, in which the arithmetic mean of the positive values of theradii of curvature of the innermost surfaces of the doublet components lies between .11 F and .25 F.

12. An optical objective as claimed in claim 8, in which the arithmetic mean of the positive values of the radii of curvature of the outermost surfaces of the doublet components lies between .17 F and .30 F.

13. An optical objective, corrected for spherical and chromatic aberrations, coma, astigmatism, field curvature and distortion, to cover a semiangular field not greater than 30 degrees, and comprising two doublet divergent outer components each having an outer convergent element and an inner divergent element, two simple convergent inner components located between such outer components, and a diaphragm located between the two inner components, said components and diaphragm being air spaced in axial alinement and all four components being of meniscus form with their air-exposed surfaces concave towards the diaphragm, the arithmetic mean of the curvatures of the internal contacts in the doublet components (a curvature being reckoned for this purpose as positive when the internal contact is concave towards the diaphragm) being algebraicly less than +3.5/F where F is the equivalent focal length of the objective and greater than 2(10:t-1)/(10x+1)F, where :c is the positive value of the difference between the arithmetic mean of the mean refractive indices of the materials of the convergent elements of the two doublet components and the arithmetic mean of the mean refractive indices of the materials of the two divergent elements, the Petzval curvature as determined from the expression 2(N N) /N .N.R having a value lying between .08/F and .16/F where the symbol 2 indicates the sum of the values of the expression following it for all the surfaces of the objective and N and N are the mean refractive indices of the materials respectively behind and in front of the surface while R is the radius of curvature of the surface and for this purpose is reckoned as positive when the surface is convex towards the front of the objective, the said difference a: being greater than .025 while the arithmetic mean of the mean refractive indices of the materials of the two simple components lies between 1.55 and 1.68 and the arithmetic mean of the mean refractive indices of the materials of the convergent elements of the two doublet components is greater than that of the divergent elements in such components.

14. An optical objective as claimed in claim 13, in which the arithmetic mean of the axial thicknesses of the two doublet components lies'between .075 F and .16 F.

15. An optical objective as claimed in claim 13, in which the arithmetic mean of the positive values of the radii of curvature of the outer surfaces of the simple inner components lies between .22 F and .44 F.

16. An optical objective as claimed in claim 13, in which the arithmetic mean of the positive values of the radii of curvature of the innermost surfaces of the doublet components lies between .11 F and .25 F.

11 12 17. An optical objective as claimed in claim 13, UNITED STATES PATENTS in which the arithmetic mean of the positive Number Name Date values 01 the radii of curvature of the outermost 1 792 917 Merte 7 17 1931 surfaces of the doublet components lies between .17 F and .30 F. 5 FOREIGN PATENTS GORDON HENRY COOK. Number Country Date 135,853 Great Britain Nov. 26, 1919 REFERENCES CITED 278,338 Great Britain Dec. 8. 1927 295,519 Great Britain Aug. 16, 1928 The following references are of record in the 10 547,739 Great Britain Sept 9, 1942 me this patent: 592,144 Great Britain Sept. 9, 1947 

